Corneal sphere tracking for generating an eye model

ABSTRACT

A head mounted display (HMD) comprises an eye tracking system configured to enable eye-tracking using light. The eye tracking system comprises two or more illumination sources positioned relative to one another and an optical detector in order to capture. The optical detector is configured to capture images of the cornea based on one or more reflections. The eye tracking unit is configured to generate a model of the user&#39;s eye. The generated eye model is used to determine eye tracking information such as gaze direction as the user glances at different objects in the HMD.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Application No. 62/306,758, filed Mar. 11, 2016 which is incorporated by reference in its entirety.

BACKGROUND

The present disclosure generally relates to eye tracking, and specifically to corneal sphere tracking for generating an eye model.

Eye tracking is an important feature for head-mounted display (HMD) systems including systems used in virtual reality (VR) applications. Conventional tracking systems track features of the human eye and are typically limited by the quality of the optical path. These conventional systems do not provide sufficient accuracy needed for eye tracking in a HMD system.

SUMMARY

An eye tracking system for generating an eye model is disclosed. The eye tracking system can be used in a VR system environment or other system environments, such as an augmented reality (AR) system. The eye tracking system includes at least two illumination sources and an optical sensor for modeling each eye. The optical sensor and the at least two illumination sources are positioned relative to each other such that the optical sensor is able to capture images of the illumination sources using reflections from the cornea of the eye (hereinafter referred to as “corneal reflections”). The system gathers data as the user moves their eyes (e.g., during a calibration process that generates the eye model and/or during normal use). The system models the eye by determining radius and origin of a corneal sphere for each eye based on the gathered data, where each eye is approximated as two spheres with one sphere approximating a portion of a scleral surface of the eye and a portion of the other sphere (i.e., corneal sphere) approximating a portion of the cornea. The system uses the eye model to perform various optical actions such as determining the user's gaze direction, vergence angle/depth, and accommodation depth.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a system environment including a VR system, in accordance with an embodiment.

FIG. 2A is a diagram of a VR headset, in accordance with an embodiment.

FIG. 2B is a cross section of a front rigid body of the VR headset in FIG. 2A, in accordance with an embodiment.

FIG. 3 depicts an example eye tracking system for generating an eye model, in accordance with an embodiment.

FIG. 4 is a flowchart of an example process for generating an eye model using an eye tracking system, in accordance with an embodiment.

FIG. 5 is a flowchart of an example process for determining a user's gaze direction using an eye model, in accordance with an embodiment.

The figures depict embodiments of the present disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles, or benefits touted, of the disclosure described herein.

DETAILED DESCRIPTION

System Overview

FIG. 1 is a block diagram of a VR system environment 100 in which a VR console 110 operates. The system environment 100 shown by FIG. 1 comprises a VR headset 105, an imaging device 135, and a VR input interface 140 that are each coupled to the VR console 110. While FIG. 1 shows an example system 100 including one VR headset 105, one imaging device 135, and one VR input interface 140, in other embodiments any number of these components may be included in the system 100. For example, there may be multiple VR headsets 105 each having an associated VR input interface 140 and being monitored by one or more imaging devices 135, with each VR headset 105, VR input interface 140, and imaging devices 135 communicating with the VR console 110. In alternative configurations, different and/or additional components may be included in the system environment 100.

The VR headset 105 is a HMD that presents content to a user. Examples of content presented by the VR head set include one or more images, video, audio, or some combination thereof. In some embodiments, audio is presented via an external device (e.g., speakers and/or headphones) that receives audio information from the VR headset 105, the VR console 110, or both, and presents audio data based on the audio information. An embodiment of the VR headset 105 is further described below in conjunction with FIGS. 2A and 2B. The VR headset 105 may comprise one or more rigid bodies, which may be rigidly or non-rigidly coupled to each other together. A rigid coupling between rigid bodies causes the coupled rigid bodies to act as a single rigid entity. In contrast, a non-rigid coupling between rigid bodies allows the rigid bodies to move relative to each other.

The VR headset 105 includes an electronic display 115, an optics block 118, one or more locators 120, one or more position sensors 125, an inertial measurement unit (IMU) 130, and an eye tracking system 160. The electronic display 115 displays images to the user in accordance with data received from the VR console 110. In various embodiments, the electronic display 115 may comprise a single electronic display or multiple electronic displays (e.g., a display for each eye of a user). Examples of the electronic display 115 include: a liquid crystal display (LCD), an organic light emitting diode (OLED) display, an active-matrix organic light-emitting diode display (AMOLED), some other display, or some combination thereof.

The optics block 118 magnifies received light from the electronic display 115, corrects optical errors associated with the image light, and the corrected image light is presented to a user of the VR headset 105. An optical element may be an aperture, a Fresnel lens, a convex lens, a concave lens, a filter, or any other suitable optical element that affects the image light emitted from the electronic display 115. Moreover, the optics block 118 may include combinations of different optical elements. In some embodiments, one or more of the optical elements in the optics block 118 may have one or more coatings, such as anti-reflective coatings.

Magnification of the image light by the optics block 118 allows the electronic display 115 to be physically smaller, weigh less, and consume less power than larger displays. Additionally, magnification may increase a field of view of the displayed content. For example, the field of view of the displayed content is such that the displayed content is presented using almost all (e.g., 110 degrees diagonal), and in some cases all, of the user's field of view. In some embodiments, the optics block 118 is designed so its effective focal length is larger than the spacing to the electronic display 115, which magnifies the image light projected by the electronic display 115. Additionally, in some embodiments, the amount of magnification may be adjusted by adding or removing optical elements.

The optics block 118 may be designed to correct one or more types of optical errors in addition to fixed pattern noise (i.e., the screen door effect). Examples of optical errors include: two-dimensional optical errors, three-dimensional optical errors, or some combination thereof. Two-dimensional errors are optical aberrations that occur in two dimensions. Example types of two-dimensional errors include: barrel distortion, pincushion distortion, longitudinal chromatic aberration, transverse chromatic aberration, or any other type of two-dimensional optical error. Three-dimensional errors are optical errors that occur in three dimensions. Example types of three-dimensional errors include spherical aberration, comatic aberration, field curvature, astigmatism, or any other type of three-dimensional optical error. In some embodiments, content provided to the electronic display 115 for display is pre-distorted, and the optics block 118 corrects the distortion when it receives image light from the electronic display 115 generated based on the content.

The locators 120 are objects located in specific positions on the VR headset 105 relative to one another and relative to a specific reference point on the VR headset 105. A locator 120 may be a light emitting diode (LED), a corner cube reflector, a reflective marker, a type of light source that contrasts with an environment in which the VR headset 105 operates, or some combination thereof. In embodiments where the locators 120 are active (i.e., an LED or other type of light emitting device), the locators 120 may emit light in the visible band (˜380 nm to 750 nm), in the infrared (IR) band (˜750 nm to 1 mm), in the ultraviolet band (10 nm to 380 nm), some other portion of the electromagnetic spectrum, or some combination thereof.

In some embodiments, the locators 120 are located beneath an outer surface of the VR headset 105, which is transparent to the wavelengths of light emitted or reflected by the locators 120 or is thin enough not to substantially attenuate the wavelengths of light emitted or reflected by the locators 120. Additionally, in some embodiments, the outer surface or other portions of the VR headset 105 are opaque in the visible band of wavelengths of light. Thus, the locators 120 may emit light in the IR band under an outer surface that is transparent in the IR band but opaque in the visible band.

The IMU 130 is an electronic device that generates fast calibration data based on measurement signals received from one or more of the position sensors 125. A position sensor 125 generates one or more measurement signals in response to motion of the VR headset 105. Examples of position sensors 125 include: one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor that detects motion, a type of sensor used for error correction of the IMU 130, or some combination thereof. The position sensors 125 may be located external to the IMU 130, internal to the IMU 130, or some combination thereof.

Based on the one or more measurement signals from one or more position sensors 125, the IMU 130 generates fast calibration data indicating an estimated position of the VR headset 105 relative to an initial position of the VR headset 105. For example, the position sensors 125 include multiple accelerometers to measure translational motion (forward/back, up/down, left/right) and multiple gyroscopes to measure rotational motion (e.g., pitch, yaw, roll). In some embodiments, the IMU 130 rapidly samples the measurement signals and calculates the estimated position of the VR headset 105 from the sampled data. For example, the IMU 130 integrates the measurement signals received from the accelerometers over time to estimate a velocity vector and integrates the velocity vector over time to determine an estimated position of a reference point on the VR headset 105. Alternatively, the IMU 130 provides the sampled measurement signals to the VR console 110, which determines the fast calibration data. The reference point is a point that may be used to describe the position of the VR headset 105. While the reference point may generally be defined as a point in space; however, in practice the reference point is defined as a point within the VR headset 105 (e.g., a center of the IMU 130).

The IMU 130 receives one or more calibration parameters from the VR console 110. As further discussed below, the one or more calibration parameters are used to maintain tracking of the VR headset 105. Based on a received calibration parameter, the IMU 130 may adjust one or more IMU parameters (e.g., sample rate). In some embodiments, certain calibration parameters cause the IMU 130 to update an initial position of the reference point so it corresponds to a next calibrated position of the reference point. Updating the initial position of the reference point as the next calibrated position of the reference point helps reduce accumulated error associated with the determined estimated position. The accumulated error, also referred to as drift error, causes the estimated position of the reference point to “drift” away from the actual position of the reference point over time.

The eye tracking system 160 generates the eye model using an example calibration process. The eye tracking system 160 includes an eye tracking unit and a control module. The eye tracking unit is located within the VR headset 105 and includes, among other components, illumination sources and optical sensors. The illumination sources (e.g., point light sources) and optical sensors (e.g., camera) of the eye tracking unit are used for corneal sphere tracking to determine a model of an eye of a user while the user is wearing the VR headset 105. The illumination sources and the optical sensors are coupled to the control module that performs the necessary data processing for generating the eye model and perform optical actions. The control module is located within the VR headset 105 and/or the VR console 110.

The imaging device 135 generates slow calibration data in accordance with calibration parameters received from the VR console 110. Slow calibration data includes one or more images showing observed positions of the locators 120 that are detectable by the imaging device 135. The imaging device 135 may include one or more cameras, one or more video cameras, any other device capable of capturing images including one or more of the locators 120, or some combination thereof. Additionally, the imaging device 135 may include one or more filters (e.g., used to increase signal to noise ratio). The imaging device 135 is configured to detect light emitted or reflected from locators 120 in a field of view of the imaging device 135. In embodiments where the locators 120 include passive elements (e.g., a retroreflector), the imaging device 135 may include a light source that illuminates some or all of the locators 120, which retro-reflect the light towards the light source in the imaging device 135. Slow calibration data is communicated from the imaging device 135 to the VR console 110, and the imaging device 135 receives one or more calibration parameters from the VR console 110 to adjust one or more imaging parameters (e.g., focal length, focus, frame rate, ISO, sensor temperature, shutter speed, aperture, etc.).

The VR input interface 140 is a device that allows a user to send action requests to the VR console 110. An action request is a request to perform a particular action. For example, an action request may be to start or end an application or to perform a particular action within the application. The VR input interface 140 may include one or more input devices. Example input devices include: a keyboard, a mouse, a game controller, or any other suitable device for receiving action requests and communicating the received action requests to the VR console 110. An action request received by the VR input interface 140 is communicated to the VR console 110, which performs an action corresponding to the action request. In some embodiments, the VR input interface 140 may provide haptic feedback to the user in accordance with instructions received from the VR console 110. For example, haptic feedback is provided when an action request is received, or the VR console 110 communicates instructions to the VR input interface 140 causing the VR input interface 140 to generate haptic feedback when the VR console 110 performs an action.

The VR console 110 provides content to the VR headset 105 for presentation to the user in accordance with information received from one or more of: the imaging device 135, the VR headset 105, and the VR input interface 140. In the example shown in FIG. 1, the VR console 110 includes an application store 145, a tracking module 150, and a VR engine 155. Some embodiments of the VR console 110 have different modules than those described in conjunction with FIG. 1. Similarly, the functions further described below may be distributed among components of the VR console 110 in a different manner than is described here.

The application store 145 stores one or more applications for execution by the VR console 110. An application is a group of instructions, that when executed by a processor, generates content for presentation to the user. Content generated by an application may be in response to inputs received from the user via movement of the VR headset 105 or the VR interface device 140. Examples of applications include: gaming applications, conferencing applications, video playback application, or other suitable applications.

The tracking module 150 calibrates the VR system 100 using one or more calibration parameters and may adjust one or more calibration parameters to reduce error in determination of the position of the VR headset 105. For example, the tracking module 150 adjusts the focus of the imaging device 135 to obtain a more accurate position for observed locators on the VR headset 105. Moreover, calibration performed by the tracking module 150 also accounts for information received from the IMU 130. Additionally, if tracking of the VR headset 105 is lost (e.g., the imaging device 135 loses line of sight of at least a threshold number of the locators 120), the tracking module 140 re-calibrates some or the entire system environment 100.

The tracking module 150 tracks movements of the VR headset 105 using slow calibration information from the imaging device 135. The tracking module 150 determines positions of a reference point of the VR headset 105 using observed locators from the slow calibration information and a model of the VR headset 105. The tracking module 150 also determines positions of a reference point of the VR headset 105 using position information from the fast calibration information. Additionally, in some embodiments, the tracking module 150 may use portions of the fast calibration information, the slow calibration information, or some combination thereof, to predict a future location of the headset 105. The tracking module 150 provides the estimated or predicted future position of the VR headset 105 to the VR engine 155.

The VR engine 155 executes applications within the system environment 100 and receives position information, acceleration information, velocity information, predicted future positions, or some combination thereof of the VR headset 105 from the tracking module 150. Based on the received information, the VR engine 155 determines content to provide to the VR headset 105 for presentation to the user. For example, if the received information indicates that the user has looked to the left, the VR engine 155 generates content for the VR headset 105 that mirrors the user's movement in a virtual environment. Additionally, the VR engine 155 performs an action within an application executing on the VR console 110 in response to an action request received from the VR input interface 140 and provides feedback to the user that the action was performed. The provided feedback may be visual or audible feedback via the VR headset 105 or haptic feedback via the VR input interface 140.

FIG. 2A is a diagram of a VR headset, in accordance with an embodiment. The VR headset 200 is an embodiment of the VR headset 105, and includes a front rigid body 205 and a band 210. The front rigid body 205 includes the electronic display 115 (not shown in FIG. 2A), the IMU 130, the one or more position sensors 125, and the locators 120. In the embodiment shown by FIG. 2A, the position sensors 125 are located within the IMU 130, and neither the IMU 130 nor the position sensors 125 are visible to the user.

The locators 120 are located in fixed positions on the front rigid body 205 relative to one another and relative to a reference point 215. In the example of FIG. 2A, the reference point 215 is located at the center of the IMU 130. Each of the locators 120 emit light that is detectable by the imaging device 135. Locators 120, or portions of locators 120, are located on a front side 220A, a top side 220B, a bottom side 220C, a right side 220D, and a left side 220E of the front rigid body 205 in the example of FIG. 2A.

FIG. 2B is a cross section 225 of the front rigid body 205 of the embodiment of a VR headset 200 shown in FIG. 2A. As shown in FIG. 2B, the front rigid body 205 includes an optical block 230 that provides altered image light to an exit pupil 250. The exit pupil 250 is the location of the front rigid body 205 where a user's eye 245 is positioned. For purposes of illustration, FIG. 2B shows a cross section 225 associated with a single eye 245, but another optical block, separate from the optical block 230, provides altered image light to another eye of the user.

The optical block 230 includes an electronic display element 235 of the electronic display 115, the optics block 118, and an eye tracking unit 260. The electronic display element 235 emits image light toward the optics block 118. The optics block 118 magnifies the image light, and in some embodiments, also corrects for one or more additional optical errors (e.g., distortion, astigmatism, etc.). The optics block 118 directs the image light to the exit pupil 250 for presentation to the user.

The VR headset 200 includes an eye tracking unit 260 (e.g., the eye tracking unit of the eye tracking system 160 of FIG. 1). The eye tracking unit 260 includes illumination sources and optical sensors. In one embodiment, the eye tracking unit 260, as shown in FIG. 2B, includes two illumination sources 262 and 264, and an optical sensor 266 for each eye. The illumination sources and the optical sensor of the eye tracking unit 260 are coupled to a control module (not shown in FIG. 2B) that performs the necessary data processing for generating the eye model. The control module is located within the VR headset 105 and/or the VR console 110. Also, in some embodiments, there is at least one eye tracking unit 260 for the left eye of the user and at least one eye tracking unit 260 for the right eye of the user.

The illumination sources 262 and 264 and optical sensor 266 are used for corneal sphere tracking of a user's eye. The eye tracking unit 260 is positioned within the optical block 230 such that the optical sensor 266 (e.g., camera) can capture images of the user's eye (and specifically cornea of the eye) over a range of eye motion. The illumination sources 262 and 264 emit light such that when the emitted light reflects off of the user's eye while the user views the emitted light, the optical sensor 266 captures one or more images of the user's eye. The eye tracking unit 260 is positioned within the optical block 230 such that light emitted from the illumination sources 262 and 264 reaches the user's eye through the optics block 118. The eye tracking unit 260 may be positioned either on-axis along the user's vision (e.g., as shown in FIG. 2B) or can be placed off-axis from the user's vision (e.g., to the left of the optics block 118). An example corneal sphere tracking system is described further below with reference to FIG. 3.

Eye Tracking System for Generating Eye Model

FIG. 3 depicts an example eye tracking system 300, in accordance with an embodiment. In some embodiments, the eye tracking system 300 is part of the eye tracking system 160 in the VR headset 105. In alternate embodiments, the eye tacking system 300 is part of some other device, e.g., a heads up display in an AR system, or some other system utilizing eye tracking. The eye tracking system 300 includes, among other components, an eye tracking unit 360 and a control module 370. For simplification, the discussion of the eye tracking system 300 is with regard to a single eye of the user. However, in some embodiments, corresponding eye tracking units 360 may be employed for each of the user's eyes. In such embodiments, a single control module 370 may control the multiple eye tracking units 360.

The eye tracking unit 360 includes, among other components, two or more illumination sources (e.g., illumination sources 362 and 364) and one or more optical sensors (e.g., optical sensor 366). The illumination sources (e.g., point light sources) and optical sensors (e.g., camera) of the eye tracking unit are used for corneal sphere tracking and to determine a model of an eye of a user while the user is wearing the VR headset 105. The illumination sources 362 and 364 have well-known emission characteristics such as ideal point light sources. In one embodiment, two illumination sources are used. Alternatively, more than two illumination sources, such as, a ring of illumination sources are used. For example, the ring of illumination sources can be positioned either in the same two-dimensional plane or in arbitrary positions relative to a reference point (e.g., location of an entrance pupil of the HMD or reference point 215). In one embodiment, the illumination sources can be located outside of the user's line of sight. Illumination sources positioned arbitrarily from the reference point can be placed at different depths from the reference point and/or at non-uniform spacing between the sources to improve the accuracy of the eye tracking.

In some embodiments, the two or more illumination sources comprise different characteristics for either all of the illumination sources or between the illumination sources. For example, light originating from the two or more illumination sources can include one or more of: different wavelengths, modulated at different frequencies or amplitudes (i.e., varying intensity), have different temporal coherence that describes the correlation between the two light waves at different points in time, and multiplexed in either time or frequency domain.

The optical sensor 366 captures images of the user's eye to capture corneal reflections. For example, the optical sensor 366 is a camera that can capture still pictures or video. The optical sensor 366 has a plurality of parameters such as focal length, focus, frame rate, ISO, sensor temperature, shutter speed, aperture, resolution, etc. In some embodiments, the optical sensor 366 has a high frame rate and high resolution. The optical sensor 366 can capture either two-dimensional images or three-dimensional images. The optical sensor 366 is placed such that the corneal reflections in response to the light from the illumination sources incident upon the eye can be captured over a range of eye movements (e.g., a maximum possible range). For example, when a ring of illumination sources are placed around the eye, the optical sensor 366 is placed pointed towards the eye around the center of the ring (e.g., in the line of sight of the user). Alternatively, the optical sensor 366 is placed off-axis such that it is outside of the main line of sight of the user. In one embodiment, more than one optical sensor 366 can be used per eye to capture corneal reflections of the eye while light from illumination sources is incident upon the eye. The optical sensor 366 may be a detector that can measure a direction of corneal reflections such as column sensors, waveguides, and the like.

The illumination sources 362 and 364 emit light that is reflected at the cornea, which is then captured (e.g., as an image) at the optical sensor 366. For example, light rays represented by arrows 362-I and 364-I originating at the illumination sources 362 and 364 are incident upon the eye. When light is incident upon the human eye, the eye produces multiple reflections such as a reflection from the outer surface of the cornea and another reflection from the inner surface of the cornea. In one embodiment, the optical sensor 366 captures the reflected light from the outer surface of the cornea in the captured images. For example, reflected light represented by arrows 362-R and 364-R is captured in images captured by the optical sensor 366. Alternatively or additionally, the optical sensor 366 captures the reflected light from the inner surface of the cornea. The reflections from the cornea (e.g., from inner surface and/or outer surface) are herein referred to as corneal reflections. An example process of generating an eye model using corneal sphere eye tracking is further described below with reference to FIG. 4.

The control module 370 generates eye models and performs optical actions. For example, the control module 370 performs the calibration to generate an eye model for one or both of a user's eyes. In some embodiments, a single control module 370 may control the multiple eye tracking units 360 such as one eye tracking unit 360 for the left eye and another eye tracking unit 360 for the right eye.

An example calibration process, described below in conjunction with FIG. 4, includes the steps of turning on the illumination sources 362 and 364, capturing images including corneal reflections at the optical sensor 366 while the user is viewing known locations on the VR headset 105, and further processing of the captured images to generate an eye model. An example normal mode of operation, described below in conjunction with FIG. 5, includes capturing corneal reflections at the optical sensor 366 while the user is viewing content on the VR headset 105 in the normal mode of operation and processing of the captured images to perform one or more optical actions such as determining a user's gaze direction. The control module 370 is located at the VR headset 105 and/or the VR console 110. The control module 370 is coupled with the eye tracking unit 360 such that the illumination sources 362 and 364, and optical sensor 366 can communicate with the control module 370.

The eye tracking system 300 generates a model for the user's eye. In one embodiment, the user's eye is modeled as two spheres 305 and 310 of different radii, where sphere 305 approximates a portion of the scleral surface of the eye (e.g., overall eye) and a portion of sphere 310 approximates the cornea of the eye. The center (or origin) of the sphere 305 is represented by point 306 and the center of corneal sphere 310 is represented by point 311. Element 315 represents the lens of the eye. In other embodiments, the cornea may be modeled as a complex surface.

The human eye can be modeled using two spheres with a bigger sphere (i.e., sphere 305) representing an approximation a portion of the scleral surface of the eye (e.g., overall eye) and a smaller sphere (i.e., sphere 310) representing an approximation of a portion of the cornea of the eye, where the two spheres have different radii and their centers are offset from each other. While it is known that the cornea forms only a small curved portion in the eye and is not a sphere in and off itself, the cornea can be approximated as a portion of a sphere. In one embodiment, the sphere 305 has a radius of approximately 25 mm and corneal sphere 310 has a radius of approximately 8 mm. The centers of the sphere 305 and sphere 310 are offset from each other as shown in FIG. 3. When the eye rotates while viewing content on a head mounted display (e.g., a VR headset 105), the rotation of the eye causes a corresponding displacement of the center of the corneal sphere 310 (i.e., point 311). The tracking system 300 tracks the motion of the center of the corneal sphere 310 during the rotation of the eye. In some embodiments, the eye tracking system 300 generates a model for a single eye of the user as described below in conjunction with FIG. 4. The generated eye model includes eye information including but not limited to radius and origin information for the corneal sphere 310, which is referred herein as “eye model information.” Alternatively or additionally, the eye model information may include radius and origin information of the sphere that approximates a portion of the scleral of the eye (i.e., sphere 305). In one embodiment, the corneal motion may be modeled as a rotation about the fixed center 306 of sphere 305. In other embodiments, the center 306 of sphere 305 is a function of the cornea position (modeling aspheric eye shapes, oculomotor muscle control, deformation under rotation, etc.). The generated eye model information is stored in a database located within the system environment 100 or outside of the system environment 100.

The control module 370 uses the stored eye models to perform one or more optical actions (e.g., estimate gaze direction for one or both eyes of the user) in the normal mode of operation while the user is viewing content. The control module 370 receives eye tracking information from the eye tracking unit 360 along with the eye model information to perform optical actions such as determining a user's gaze direction, a user's vergence angle (or vergence depth), a user's accommodation depth, identification of the user, an eye's torsional state, or some combination thereof. The control module 370 can be implemented in either hardware, software, or some combination thereof.

FIG. 4 is a flowchart of an example calibration process 400 for generating an eye model using an eye tracking system (e.g., eye tracking system 300 of FIG. 3), in accordance with an embodiment. The example calibration process 400 of FIG. 4 may be performed by the eye tracking system 300, e.g., as part of a VR headset 105 and/or the VR console 110, or some other system (e.g., an AR system). Other entities may perform some or all of the steps of the process in other embodiments. Likewise, embodiments may include different and/or additional steps, or perform the steps in different orders. The example process of FIG. 4 is for generating an eye model for one of the user's eyes and can also be implemented (either concurrently or sequentially) for determining an eye model for the user's other eye. The example process is described using two illumination sources and one optical sensor for modeling the eye. An eye model can be generated using more than two illumination sources and/or more than one optical sensor.

The eye tracking system 300 illuminates 410 the user's eye by turning on two illumination sources (e.g., illumination sources 362 and 364) that are positioned at known locations relative to, e.g., an optical sensor (e.g., optical sensor 366). These illumination sources emit light that is incident on the user's eye such that the cornea of the eye reflects the light.

The eye tracking system 300 captures 420 corneal reflections of the light incident upon the user's eye as one or more images. In one embodiment, the eye tracking system 300 captures a single image of the corneal reflections. Alternatively, the eye tracking system 300 captures multiple images of corneal reflections as the user looks at a sequence of known targets (e.g., specific points on the electronic display 235).

The eye tracking system 300 generates a model of the eye, where the eye model includes radius and origin information for the corneal sphere 310. The captured one or more images including corneal reflections of light originating from the two illuminations sources at known locations results in a single corneal radius and a corneal sphere origin that fits the data of the captured images. In one embodiment, the eye tracking system 300 generates the eye model by using a learning model that uses a reference eye. The reference eye, as referred to herein, is an eye with a reference eye model that includes known radius and origin information for each of corneal sphere (e.g., sphere 310) and the sphere representing the a portion of the scleral surface of the eye (e.g., sphere 305). The learning model includes capturing the corneal reflections of the reference eye while the reference eye is rotated to emulate a range of human eye movements. The learning model includes the relationship between various movements of the reference eye and the corneal reflections of the reference eye, and such relationship is used to generate the eye model for the user's eye. For example, the corneal reflections of the user's eye captured in step 420 are compared with that of the corneal reflections of the reference eye to extrapolate different parameters for the eye model (e.g., radius and origin) for the corneal sphere 310 of the user's eye. In such example, the radius and origin information of the reference eye model of the learning model is extrapolated to estimate radius and origin information for the user's eye model. An example method of estimating the radius and origin for the eye model is described below.

The eye tracking system 300 determines 430 a radius of the corneal sphere 310 based on the captured images that include corneal reflections of at least two of the illuminating sources. Each image provides sufficient information to derive an estimate of the corneal radius and corneal position. In some embodiments, the eye model may include only a sphere of fixed radius for the cornea. The corneal radius estimate may then be refined by combining estimates over a sequence of frames using an appropriate statistical model. For example, the samples of corneal radius may form a normal distribution about the mean over a sequence of images. When a sequence of images provides a set of estimations with a low variance around the mean with few outliers, the corneal radius could be assumed to be the mean of these samples. In embodiments with three or more illumination sources, the difference in corneal radius predicted by each set of two illumination sources may be used to inform a non-spherical model for the corneal surface (ex. b-splines, polynomial surface, etc.). In yet other embodiments, the difference in corneal radius predicted in a set of frames may be combined with a predicted gaze direction per frame to inform a more complex corneal model. In these systems, the cornea is defined by the reference origin 311 and an orientation.

The eye tracking system 300 determines an effective center 306 of eye rotation and a distance separating the eye rotation center and the cornea center (e.g., a distance between centers 306 and 311). In one implementation, the eye center 306 may be assumed to be a fixed point. In this system, the user may be presented with visual targets on the electronic display element 235 presented at known angular offsets from a reference position. For example, the target may be placed at a distance approaching infinity with the desired angular deviation in a distortion-corrected virtual rendered space of the HMD. The distortion-corrected virtual rendered space is a computer-generated three-dimensional representation of content on the electronic display element 235 to a user of the HMD, where the displayed content is corrected for distortion-based optical errors. The eye tracking system 300 determines and records 440 a location of the corneal sphere while the user is looking toward each of these calibration targets. This system may model the user's gaze as lying along the vector from the eye center 306 through the corneal center 311. The position of the eye center 306 and orientation of the eye to the virtual rendered space of the HMD may be inferred as the point 306 and orientation that best satisfies the assumption that the distance 306 to 311 remains unchanged and that the gaze vectors from 306 to recorded corneal centers 311 align most closely with the presented target angular offsets. In other systems, the precise eye center 306 may be modeled as a function of cornea position (and/or cornea orientation in more complex models) for the purpose of gaze estimation to model physiological deviations from a spherical eye model.

Determine User Gaze Using Eye Model

FIG. 5 is a flowchart of an example process for determining a user's gaze direction using a known eye model, in accordance with an embodiment. The example process 500 of FIG. 5 may be performed by the eye tracking system 300, e.g., as part of the VR headset 105 and/or the VR console 110 or some other system (e.g., an AR system). Other entities may perform some or all of the steps of the process in other embodiments. Likewise, embodiments may include different and/or additional steps, or perform the steps in different orders. The example process 500 describes a normal mode of operation of the eye tracking system 300 where the system is tracking eye motion of a user based in part on one or more eye models.

The eye tracking system 300 obtains 510 eye model information including radius and origin information of corneal sphere 310. In one embodiment, the eye tracking system 300 obtains the eye model information from within the eye tracking system 300 (e.g., eye tracking system 300 generates the eye model as described above in conjunction with FIG. 4). Alternatively, the eye tracking system 300 obtains the eye model information external to the eye tracking system 300 (e.g., a VR console 110 or outside of system environment 100).

The eye tracking system 300 illuminates 520 the user's eye by turning on two illumination sources (e.g., illumination sources 362 and 364) that are positioned at known locations relative to, e.g., an optical sensor (e.g., optical sensor 366). These illumination sources emit light that is incident on the user's eye such that the cornea of the eye reflects the light.

The eye tracking system 300 captures 530 one or more images of the user's cornea (i.e., corneal reflections) while the viewer is viewing content on a HMD (e.g., of a VR headset 105, an AR headset, or some other system using eye tracking). In one embodiment, the eye tracking system 300 captures a single image of the corneal reflections, where the corneal reflections include reflections of light from the two or more illumination sources. Alternatively, the eye tracking system 300 captures multiple images of corneal reflections, where the corneal reflections include reflections of light from the two or more illumination sources.

The eye tracking system 300 determines 540 a user's gaze direction using the corneal reflection data of the captured images. In one embodiment, the eye tracking system 300 extrapolates the corneal reflection data using the obtained eye model information that includes the corneal radius and origin information. For example, the eye tracking system 300 determines location data of the specific point the user is gazing upon on the electronic display 235 by casting a ray from the derived eye center 306 through the center 311 of the corneal sphere 310. The origin and direction of this ray are transformed into a three-dimensional coordinate space of the distortion-corrected virtual rendered space of the HMD using the derived orientation of the eye.

In some embodiments, the eye tracking system 300 performs other optical actions in addition or alternative to determining a user's gaze direction. Other optical actions include, e.g., determining a user's vergence angle (or vergence depth), a user's accommodation depth, identification of the user, an eye's torsional state, or some combination thereof. Some of the example optical actions might require captured corneal reflection data of both the user's eyes to perform the optical actions, and one or more steps of the example process 500 may additionally be performed for the user's other eye (either concurrently or sequentially) to perform such optical actions.

Additional Configuration Information

The foregoing description of the embodiments has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the patent rights to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure.

The language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the patent rights be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the disclosure of the embodiments is intended to be illustrative, but not limiting, of the scope of the patent rights, which is set forth in the following claims. 

What is claimed is:
 1. A head mounted display (HMD) comprising: an eye tracking system including: two or more illumination sources configured to illuminate a user's eye, a detector configured to capture one or more images of the user's eye including light reflected from a cornea of the user's eye, and a control module configured to: generate a model of the eye based on the captured one or more images of the user's eye the generated model comprising a first sphere that approximates a portion of a scleral surface of the eye and a second sphere that approximates the cornea, and perform an optical action based in part on the generated model of the eye.
 2. The HMD of claim 1, wherein the two or more illumination sources are positioned relative to one another such that the detector is able to capture one or more images of the two or more illumination sources based on the light reflected from cornea.
 3. The HMD of claim 1, wherein the two or more illumination sources are part of the electronic display.
 4. The HMD of claim 1, wherein each of the two or more illumination sources are configured to emit light of a different wavelength.
 5. The HMD of claim 1, wherein light emitted by each of the two or more illumination sources is modulated at a different frequency and a different amplitude.
 6. The HMD of claim 1, wherein the two or more illumination sources form a ring pattern.
 7. The HMD of claim 1, wherein the detector is an optical sensor that can capture a plurality of images of the user's eye.
 8. The HMD of claim 1, wherein the control module is further configured to: receive the one or more captured images of the user's eye, the images including one or more corneal reflections; generate the model of the eye, the generated model of the eye including a radius and an origin associated with the first sphere and a radius and an origin associated with the second sphere; and store the generated model in a database associated with the HMD.
 9. The HMD of claim 8, wherein the control module is further configured to model corneal motion as a rotation about the origin associated with the first sphere.
 10. The HMD of claim 1, wherein the control module is further configured to: retrieve a learning model of a reference eye, the learning model including a relationship between one or more movements of the reference eye and the corneal reflections associated with the reference eye; capture an image of the user's eye, the one or more images including a corneal reflections; and extrapolate one or more parameter values associated with the eye model based on a comparison between the one or more corneal reflections of the reference eye and the corneal reflections associated with the captured image.
 11. The HMD of claim 1, wherein an optical action is selected from a group consisting of: determining a user's vergence angle, determining a user's accommodation depth, identifying the user, determining an eye's torsional state, or some combination thereof.
 12. A head mounted display (HMD) comprising: an electronic display configured to display images to the user; an optics block configured to magnify light received by the optics block from the electronic display; and an eye tracking system including: two or more illumination sources configured to illuminate a surface of an eye of the user, a detector configured to capture one or more images of the user's eye including light reflected from the cornea of the user's eye, and a control module configured to: generate a model of the eye based on the captured one or more images of the user's eye, the generated model comprising a first sphere that approximates a portion of a scleral surface of the eye and a second sphere that approximates the cornea, and perform an optical action based in part on the generated model of the eye.
 13. The HMD of claim 12, wherein the two or more illumination sources are positioned relative to one another such that the detector is able to capture one or more images of the two or more illumination sources based on the light reflected from cornea.
 14. The HMD of claim 12, wherein the two or more illumination sources are part of the electronic display.
 15. The HMD of claim 12 , wherein the control module is further configured to: receive the one or more captured images of the user's eye, the images including one or more corneal reflections; generate the model of the eye, the generated model of the eye including a radius and an origin associated with the first sphere and a radius and an origin associated with the second sphere; and store the generated model in a database associated with the HMD.
 16. The HMD of claim 15, wherein the control module is further configured to model corneal motion as a rotation about the origin associated with the first sphere.
 17. the HMD of claim 12, wherein the control module is further configured to: retrieve a learning model of a reference eye, the learning model including a relationship between one or more movements of the reference eye and the corneal reflections associated with the reference eye; capture an image of the user's eye, the one or more images including a corneal reflections; and extrapolate one or more parameter values associated with the eye model based on a comparison between the one or more corneal reflections of the reference eye and the corneal reflections associated with the captured image.
 18. The HMD of claim 12, wherein an optical action is selected from a group consisting of: determining a user's vergence angle, determining a user's accommodation depth, identifying the user, determining an eye's torsional state, or some combination thereof.
 19. A method comprising: illuminating a user's eye with light from two or more illumination sources; capturing, at a detector, one or more images of the illuminated user's eye, the one or more images including light reflected from a cornea of the user's eye; generating a model of the user's eye based on the captured one or more images of the user's eye, the generated model comprises a first sphere that approximates a portion of a scleral surface of the eye and a second sphere that approximates the cornea; and performing an optical action based in part on the generated model of the eye.
 20. The method of claim 19, wherein the two or more illumination sources are positioned relative to one another such that the detector is able to capture one or more images of the two or more illumination sources based on the light reflected from cornea.
 21. The method of claim 19, wherein the two or more illumination sources are part of the electronic display.
 22. The method of claim 19, wherein illuminating a user's eye with light from two or more illumination sources comprises illuminating the user's eye with at least two different wavelengths of light.
 23. The method of claim 19, wherein light emitted by each of the two or more illumination sources is modulated at a different frequency and a different amplitude.
 24. The method of claim 19, wherein the two or more illumination sources form a ring pattern.
 25. The method of claim 19, wherein the detector is an optical sensor that can capture a plurality of images of the user's eye.
 26. The method of claim 19 further comprising: receiving the one or more captured images of the user's eye, the images including one or more corneal reflections; generating the model of the eye, the generated model of the eye including a radius and an origin associated with the first sphere and a radius and an origin associated with the second sphere; and storing the generated model in a database associated with the HMD.
 27. The method of claim 26 further comprising: modeling corneal motion as a rotation about the origin associated with the first sphere.
 28. The method of claim 19 further comprising: retrieving a learning model of a reference eye, the learning model including a relationship between one or more movements of the reference eye and the corneal reflections associated with the reference eye; capturing an image of the user's eye, the one or more images including a corneal reflections; and extrapolating one or more parameter values associated with the eye model based on a comparison between the one or more corneal reflections of the reference eye and the corneal reflections associated with the captured image.
 29. The method of claim 19, wherein an optical action is selected from a group consisting of: determining a user's vergence angle, determining a user's accommodation depth, identifying the user, determining an eye's torsional state, or some combination thereof. 